feat(pipeline): add unified pipeline architecture with Stage abstraction

- Add engine/pipeline/ module with Stage ABC, PipelineContext, PipelineParams
- Stage provides unified interface for sources, effects, displays, cameras
- Pipeline class handles DAG-based execution with dependency resolution
- PipelinePreset for pre-configured pipelines (demo, poetry, pipeline, etc.)
- Add PipelineParams as params layer for animation-driven config
- Add StageRegistry for unified stage registration
- Add sources_v2.py with DataSource.is_dynamic property
- Add animation.py with Preset and AnimationController
- Skip ntfy integration tests by default (require -m integration)
- Skip e2e tests by default (require -m e2e)
- Update pipeline.py with comprehensive introspection methods

engine/pipeline/registry.py

@@ -0,0 +1,127 @@
+"""
+Stage registry - Unified registration for all pipeline stages.
+
+Provides a single registry for sources, effects, displays, and cameras.
+"""
+
+from __future__ import annotations
+
+from engine.pipeline.core import Stage
+
+
+class StageRegistry:
+    """Unified registry for all pipeline stage types."""
+
+    _categories: dict[str, dict[str, type[Stage]]] = {}
+    _discovered: bool = False
+    _instances: dict[str, Stage] = {}
+
+    @classmethod
+    def register(cls, category: str, stage_class: type[Stage]) -> None:
+        """Register a stage class in a category.
+
+        Args:
+            category: Category name (source, effect, display, camera)
+            stage_class: Stage subclass to register
+        """
+        if category not in cls._categories:
+            cls._categories[category] = {}
+
+        # Use class name as key
+        key = stage_class.__name__
+        cls._categories[category][key] = stage_class
+
+    @classmethod
+    def get(cls, category: str, name: str) -> type[Stage] | None:
+        """Get a stage class by category and name."""
+        return cls._categories.get(category, {}).get(name)
+
+    @classmethod
+    def list(cls, category: str) -> list[str]:
+        """List all stage names in a category."""
+        return list(cls._categories.get(category, {}).keys())
+
+    @classmethod
+    def list_categories(cls) -> list[str]:
+        """List all registered categories."""
+        return list(cls._categories.keys())
+
+    @classmethod
+    def create(cls, category: str, name: str, **kwargs) -> Stage | None:
+        """Create a stage instance by category and name."""
+        stage_class = cls.get(category, name)
+        if stage_class:
+            return stage_class(**kwargs)
+        return None
+
+    @classmethod
+    def create_instance(cls, stage: Stage | type[Stage], **kwargs) -> Stage:
+        """Create an instance from a stage class or return as-is."""
+        if isinstance(stage, Stage):
+            return stage
+        if isinstance(stage, type) and issubclass(stage, Stage):
+            return stage(**kwargs)
+        raise TypeError(f"Expected Stage class or instance, got {type(stage)}")
+
+    @classmethod
+    def register_instance(cls, name: str, stage: Stage) -> None:
+        """Register a stage instance by name."""
+        cls._instances[name] = stage
+
+    @classmethod
+    def get_instance(cls, name: str) -> Stage | None:
+        """Get a registered stage instance by name."""
+        return cls._instances.get(name)
+
+
+def discover_stages() -> None:
+    """Auto-discover and register all stage implementations."""
+    if StageRegistry._discovered:
+        return
+
+    # Import and register all stage implementations
+    try:
+        from engine.sources_v2 import (
+            HeadlinesDataSource,
+            PipelineDataSource,
+            PoetryDataSource,
+        )
+
+        StageRegistry.register("source", HeadlinesDataSource)
+        StageRegistry.register("source", PoetryDataSource)
+        StageRegistry.register("source", PipelineDataSource)
+    except ImportError:
+        pass
+
+    try:
+        from engine.effects.types import EffectPlugin  # noqa: F401
+    except ImportError:
+        pass
+
+    try:
+        from engine.display import Display  # noqa: F401
+    except ImportError:
+        pass
+
+    StageRegistry._discovered = True
+
+
+# Convenience functions
+def register_source(stage_class: type[Stage]) -> None:
+    """Register a source stage."""
+    StageRegistry.register("source", stage_class)
+
+
+def register_effect(stage_class: type[Stage]) -> None:
+    """Register an effect stage."""
+    StageRegistry.register("effect", stage_class)
+
+
+def register_display(stage_class: type[Stage]) -> None:
+    """Register a display stage."""
+    StageRegistry.register("display", stage_class)
+
+
+def register_camera(stage_class: type[Stage]) -> None:
+    """Register a camera stage."""
+    StageRegistry.register("camera", stage_class)